Conventionally, an internal electrode and a ceramic layer used for ceramic electronic components have mainly been manufactured by printing methods using printing plates, such as screen printing and gravure printing. These printing methods are suitable for mass-production; however, they are not good at producing small batches of a variety of products as a trend in recent years. Responding to such demands, ink jet printing for manufacturing ceramic electronic components has been suggested as a new printing method.
First of all, ink typically used for ink jet printing will be described. Typical ink for ink jet printing falls into dye- or pigment-types that volatilize or deteriorate by baking. Therefore, they cannot be used as electrode material, dielectric material, or magnetic material. For example, U.S. Pat. No. 3,889,270 suggests ink for ink jet printing on paper and U.S. Pat. No. 4,150,997 suggests aqueous fluorescent ink for ink jet printing and its manufacturing method; both inks cannot be applied to production of electronic components because they are used for coloring. Similarly, U.S. Pat. No. 4,894,092 introduces a heat-resistant pigment; this is also for coloring, so that it cannot be employed for electronic components. U.S. Pat. No. 4,959,247 introduces electrochromic coating and a method for making the same; this cannot be applied to production of electronic components. U.S. Pat. No. 5,034,244 introduces a method of forming a heat-resistant substrate pattern for glass using an inorganic ceramic pigment; such a pigment-type ink cannot lend itself to production of electronic components.
Next will be described ink for ink jet printing that is used for coloring ceramic substrates. U.S. Pat. No. 5,273,575 suggests ink for ink jet printing that can be used for coloring, for example, in black, green, and brilliant blue, ceramic substrates. The ink is, instead of pigments, made of a solvent in which some kinds of metallic salt are dissolved. U.S. Pat. No. 5,407,474 suggests another ink for ink jet printing used for coloring ceramic substrates, in which inorganic pigment has a limited particle diameter. U.S. Pat. No. 5,714,236 suggests yet another ink for ink jet printing for coloring ceramic substrates. In this patent, the ink is made by combining some kinds of metallic salt with flammable materials that serve as an oxygen supplier. Although the inks introduced in these suggestions are capable of printing and coloring such as marking electronic components made of ceramic, they cannot be used for an internal electrode, dielectric material, and magnetic material. On the other hand, Japanese Patent Examined Publication No. H5-77474 and Japanese Patent Non-examined Publication No. S63-283981 suggest methods of decorating a ceramic substrate employing chelate with application of heat. As another example, Japanese Patent Examined Publication No. H6-21255 suggests marking ink with application of heat, which is made of silicon resin and an inorganic coloring pigment, and a solvent. As yet another example, Japanese Patent Non-examined Publication No. H5-202326 suggests ink for marking ceramic substrates in which a soluble metallic salt is employed. As still another example, Japanese Patent Non-examined Publication No. H5-262583 introduces a marking method. This method suggests that an acidic aqueous solution in which a soluble metallic salt is dissolved should be applied to a ceramic substrate, and on which an alkaline aqueous solution should be applied for neutralization of metallic salt, and then the substrate should be baked. As another example, Japanese Patent Non-examined Publication No. H7-330473 introduces a marking method. This method suggests that ink, which is made of a metallic ion aqueous solution, is jetted onto a given shape of a ceramic substrate prior to baking. As still another example, Japanese Patent Non-examined Publication No. H8-127747 suggests marking ink for coloring ceramic substrates, which contains metallic pigments therein. However, all these inks for coloring ceramics are not suitable for production of electronic components.
Now will be described examples in which an etching resist used for production of electronic components is produced by ink jetting. U.S. Pat. No. 5,567,328 suggests that ink jet printing should be employed for producing a resist pattern of an etching resist in manufacturing a circuit board. Similarly, Japanese Patent Non-examined Publication No. S60-175050 suggests that ink jet printing should be employed for producing a three-dimensional resist pattern of an etching resist on a metal-coated substrate. Employing an etching resist, however, increases a cost of manufacturing electronic components. Conventional methods of ink jet printing and inks for ink jet printing, as described above, have not achieved a low-cost-production of electronic components.
Here will be described suggestions in which ink jet printing should be employed for manufacturing a variety of electronic components. Conventionally, some attempts had been made to manufacture electronic components by using an ink jet apparatus. For example, Japanese Patent Non-examined Publication No. S58-50795 suggests a method in which a conductor or a resistor is formed on an unbaked ceramic substrate by ink jet printing. According to conventional ink jet printing, as described above, in a process of forming an electronic circuit on a substrate, the ink for forming the electronic circuit tends to flow or extend out of an intended pattern on the substrate.
Referring to FIG. 14, here will be described an ink jet apparatus used for forming electronic circuits, which is suggested in Japanese Patent Non-examined Publication No. S58-50795. FIG. 14 illustrates a problem that tends to occur in forming electronic circuits by ink jet printing. In FIG. 14, being set in ink jet nozzle 2, ink 1 for forming electronic components is jetted by pressure from air and a piezoelectric element (both are not shown) on a “drops-on-demand” basis to form droplets 3. Landed onto substrate 4, on which a circuit pattern is to be printed, droplets 3 form pattern 5 in a predetermined shape. In this process, if ink 1 has aggregates 6 therein, it can cause unstable jetting of droplets from the ink jet nozzle, which sometimes results in a failure to print. That is, pattern 5 has faulty sections 7, such as a pin hole, due to aggregates 6. The ink 1 for forming electronic components, as described above, tends to have aggregates 6 therein that often clog ink jet nozzle 2. This problem has lowered yields of electronic components.
Referring to FIG. 15, here will be described forming precipitates or aggregates developed in ink for forming electronic components. FIG. 15 shows a result derived from calculation in which behavior of a powder in a solution is substituted into theoretical expressions. In the graph of FIG. 15, the Y-axis represents velocity (cm/sec) of a powder, and the X-axis represents a particle diameter (μm) of the powder. Line 8 shows velocity of the powder derived from the formula of the Brownian movement. It is apparent that the smaller the particle diameter of the powder, the greater the velocity of the powder (i.e., the Brownian movement of the powder becomes more remarkable.) Line 9 in the graph indicates velocity of the powder derived from the Einstein-Stalks's formula. This velocity is equivalent to a sedimentation velocity of the powder in a solution. That is, the larger the particle diameter of the powder, the greater the sedimentation velocity of the powder. Point 10 is an intersection of line 8, indicating the velocity of the powder in the Brownian movement, and line 9, indicating the sedimentation velocity of the powder. In a calculation result shown in FIG. 15, the solution has a viscosity of 1 cP (mPa s). Theoretically, in area α—the left-hand portion from point 10 as viewed in FIG. 15, due to a small particle diameter, the powder is subjected to the Brownian movement (represented by line 8) larger than the sedimentation velocity (represented by line 9). That is, the powder in area α is hard to sedimentate. On the other hand, the powder in area β—the right-hand portion from point 10—is subjected to a sedimentation velocity larger than the Brownian movement, so that this powder is easy to sedimentate. Point 10 is susceptible to a specific gravity of a powder, so that a position of point 10 moves to area α, i.e., leftward as viewed in FIG. 15, as the specific gravity of the powder increases. The graph theoretically tells that any ink being within the cross-hatching area in FIG. 15, that is, the area in which line 8 representing the Brownian movement exceeds line 9 representing the sedimentation velocity, is hard to have precipitation. Therefore, such ink could be handled with an ink jet apparatus available in the market, and can be commonly used aqueous dye-type ink.
The result shown in the FIG. 15, however, is derived from a theory in an “extremely diluted” condition; practically, consideration should be given to a relationship between powders in the solution. Therefore, the ink, even if it belongs to the aforementioned area in FIG. 15, may not be handled with an ink jet apparatus available in the market. That is, ink for electronic components employing the powder, being within the cross-hatching area and therefore theoretically not having precipitation, often forms precipitates or aggregates due to a variety of factors: incomplete dispersion; aggregates from a relationship between the powders; variations in particle size distribution; and heterogeneous precipitation—a theory explaining that mixture of powders having different particle sizes easily leads to aggregation. If the ink for electronic components can be consistently manufactured to have its powder particle diameter of 0.01 μm, the ink might have precipitation less than that belonging to the cross-hatching area in FIG. 15.
Now suppose that metallic powder or ceramic powder having an average particle size of 0.01 μm is selected from those available in the market. In actuality, however, it is impossible to completely eliminate a powder having a particle size of 1 μm even after high classification. Besides, a powder tends to have aggregates (or secondary particles) therein as the particle size of the powder becomes smaller. This fact sometimes allows a powder to have secondary particles larger than 1 μm, in spite of its primary particles having an average particle size of 0.01 μm. Furthermore, it is difficult to break such a secondary particle into a smaller particle even being well dispersed, thereby inviting an increase in a processing cost for practical use. In reality, ink for electronic components having powder with a particle diameter of at least 1 μm, or particularly around 10 μm, is preferably used in terms of obtaining an intended property and low-cost product. In this case, as is apparent from FIG. 15, sedimentation velocity indicated by line 9 exceeds the Brownian movement indicated by line 8 by several digits. In addition, a powder suitable for the ink for electronic components is a ceramic powder with its specific gravity of around 3 to 7, or is a metallic material with its specific gravity of approximately 6 to 20. Taking this into account, it is almost impossible, even in theory, to have stable dispersion in a solution having a low viscosity. In some cases, ink has a powder as a mixture of powders having different particle diameters to pursue an intended property. Such ink tends to have heterogeneous aggregation, so that it is difficult to obtain a stable dispersion. Besides, a fine particle having a submicronic diameter has a large amount of oil absorption—defined in Japanese Industrial Standards (JIS)—due to its large specific surface area, and accordingly, an amount of a solvent absorbed in a surface of the powder increases. Therefore, high concentration of powders in a solvent suddenly raises a viscosity of the solvent, thereby depriving fluidity from the solvent. In general, ink for printing on paper is mainly formed of a dye. Even in a case that pigments are employed, a concentration of the powder is maintained to be not more than 5 weight %. Whereas, in a case of ink used for producing electronic components, ceramic or metallic powder materials are required because an intended property cannot be obtained from dyes or metallic salts. In addition, the ink sometimes needs such materials having a concentration of the powder of several tens weight %, thereby inviting aggregation. For this reason, it has been difficult to realize consistent printing quality.
Referring now to FIGS. 16A and 16B, problems in a case of printing by a conventional ink jet apparatus having ink for electronic components will be described. In FIG. 16A, ink tank 11 is filled with ink 12 containing powder 13. Ink 12 has aggregates 14 developed from powder 13. Ink 12 in ink tank 11 flows, together with powder 13 and aggregates 14, into an interior of printer head 16 via piping 15. In response to an external signal (not shown), ink 12 stored in printer head 16 is jetted out on a drop-on-demand basis to form droplets 17. Droplets 17 land on a surface of substrate 18 to be printed, thereby forming ink pattern 19. Arrow 20 indicates a direction of flow of ink 12 in piping 15, or a direction of flying of droplets 17 jetted from printer head 16. FIG. 16B illustrates in detail a structure of piping 15 and printer head 16 shown in FIG. 16A, with the interior of head 16 enlarged. Aggregates 14 in FIG. 16B, which are developed from the powder in ink tank 12, piping 15, or printer head 16, lowers stability during printing.
In a conventional ink jet apparatus, aggregates 14 in ink 12 accumulate in the interior of printer head 16. The greater the time required for printing or the greater the volume of printing, the greater the amount of the aggregates. Therefore, it has been difficult for the conventional apparatus to provide stable printing for long hours.
Conventional jet ink for electronic components, as described above, tends to have aggregates or precipitates therein. These aggregates and precipitates not only clog a head of an ink jet printer, but also invite unstable ink jetting and cause ill effect on a direction of ink jetting. During ink jet printing, the printer head has no contact with a surface to be printed. If the direction of jetting ink does not conform to a predetermined direction, faulty patterns—a deformed pattern, pin hole in solidly shaded areas in printing, or a short circuit in a wiring pattern—may result.
Ink 1 for electronic components set in the interior of ink jet nozzle 2, as described above, forms precipitates 14 or aggregates 14, thereby inviting various adverse effects on an ink jetting condition; clogging spout 55, non-uniform spouting of droplets 3 jetted from spout 55, inconsistent amount of spouting with passage of time, or spout 55 clogged up with precipitates 14 or aggregates 14.
Although the precipitates and the aggregates are the same, this specification differentiates, for convenience's sake, between precipitation and aggregation in such a way that one precipitated at a bottom is referred to as a precipitate, while one floating in the ink is referred to as a aggregate. The ink required for producing electronic components, as described above, tends to have precipitates and aggregates, which has been an obstacle to stabilized quality in conventional ink jet printing. Precipitates 14 and aggregates 14 can not only clog the printer head, but also invite unstable ink jetting and cause ill effect on the direction of ink jetting. In the ink jet printing, the printer head has no contact with a surface to be printed. Therefore, if a direction of spouting ink does not conform to a predetermined direction, faulty patterns—a deformed pattern, pin hole in solidly shaded areas in printing, or a short circuit in a wiring pattern—may result.
Other than the examples introduced above, there are suggestions about methods of manufacturing electronic components by ink jet printing. For example, Japanese Patent Non-examined Publication No. H8-222475 suggests a method of manufacturing thick film electronic components using an ink jet apparatus. According to this suggestion, ink suitable for the thick film, such as an electrically conductive ink and an ink for a resistance film, is applied to an internal electrode pattern having a given shape on a surface of a ceramic green sheet, and the sheet is laminated and then baked. As another example, Japanese Patent Non-examined Publication No. S59-82793 has a suggestion in which an electrically conductive adhesive or a low-temperature baking conductive paste is applied, by ink jetting, to a predetermined connecting position on a printed circuit board. As still another example, Japanese Patent Non-examined Publication No. S56-94719 discloses a method of manufacturing a reversed pattern of an internal electrode by spraying ceramic ink, which eliminates unevenness, of a surface due to thickness of internal electrodes, from a laminated ceramic capacitor. Addressing the same problem, Japanese Patent Non-examined Publication No. H9-219339 has a suggestion in which ceramic ink is applied to a surface of a ceramic green sheet by ink jet printing. However, up to now, an ink jet apparatus and ink available for such suggestions have not yet come into existence.
As a similar example, Japanese Patent Non-examined Publication No. H9-232174 suggests a method of manufacturing electronic components including a laminated inductor. In a manufacturing process, functional material paste, such as electrically conductive paste and resistance paste, is jetted out, together with ceramic paste, by an ink jet system. As a method similar to the aforementioned one in which a laminated inductor is produced without using a via hole, U.S. Pat. No. 4,322,698 introduces a method of manufacturing a laminated inductor by alternately forming layers of insulating material so as to expose a part of each coil pattern. Japanese Patent Non-examined Publication No. S48-81057 suggests a method of laminating a coil through a via hole formed in a ceramic green sheet. Further, Japanese Patent Non-examined Publication No. H2-65112 has a suggestion about improving characteristics of a semiconductive capacitor in terms of its manufacturing process. In the process, a required amount of dorpant solution is ink jetted, as a form of droplets, onto a surface of a device of a semiconductive capacitor. In this case, to prepare ink for ink jetting, metal ionic salts are dissolved in ethyl alcohol or acid for pH-control. When materials for forming electronic components are dissolved in the ink, as is the case above, neither precipitates 14 nor aggregates 14 shown in FIGS. 16A and 16B are developed in the ink. Still, the aforementioned method cannot provide electronic components as a method suggested in the present invention.
There are some suggestions about coloring a surface of ceramics or forming a predetermined image on the surface, and not forming an electronic circuit thereon. As ink for ink jet printing, a metallic ion solution is employed in Japanese Patent Non-examined Publication No. H7-330473; an organometal chelate compound is employed in Japanese Patent Non-examined Publication No. S63-283981; water glass is added to ink in Japanese Patent Examined Publication No. H5-69145; and silicon resin is added in Japanese Patent Examined Publication No. H6-21255. These forgoing suggestions are, however, aimed at forming images, not electronic circuits. Therefore, they are no help for manufacturing electronic components.
In methods of manufacturing a variety of electronic components by conventional ink jet printing, a nozzle of a printer head requires jetting ink containing powdery material that is necessary for manufacturing electronic components, such as ceramics, glass, and metal. Such powders contained in the ink have often clogged the nozzle, as described in FIGS. 14 through 16B. For this reason, almost no demonstrations in which electronic components can be manufactured by ink jet printing has been made. In particular, in a case of manufacturing a variety of electronic components, ink for ink jet printing is required to have a property suitable for each component to be manufactured. Supposing manufacturing of laminated ceramic electronic components; an ink for an internal electrode needs to contain palladium, nickel, silver palladium; an ink for a dielectric material needs dielectric material; and an ink for an external electrode needs silver.
Furthermore, a coil part needs ink for magnetic material, and a coil conductor needs ink containing silver or copper. When a chip resistor is manufactured by ink jet printing, it becomes necessary to prepare a plastic ink for ink jetting, an insulating glass-made ink, an ink for over-coating, an ink for graphic printing, a graze ink, an ink for an electrode, an ink for a resistor, and ink for an external electrode. Only for the ink for a resistor, should be prepared dozens of types of different inks that have resistance ranging from a few mΩ up to several tens of MΩ, with a temperature coefficient of resistance (TCR) adjusted within a predetermined range. The inks for ink jet printing that meet such diverse requirements neither have been commercially available, nor reported in a learned society or the like. Even if prototypes of these inks are built and tested, clogging a nozzle may result due to the problems explained in FIGS. 16A and 16B.
As for ink for printing on paper—not for manufacturing electronic components, many suggestions have been made to address the problems above. As an example of these attempts, Japanese Patent Non-examined Publication No. H5-229140 introduces a suggestion in which ink containing inorganic pigments is stirred in an ink-supplying chamber and then fed to a head of an ink jet printer.
As another example, Patent Non-examined Publication No. H5-263028 suggests that ink should be filtered by a metallic filter with application of pressure. To filter ink for manufacturing electronic components, an extremely fine filter is required. However, such a fine filter for electronic components is not available at a time of the present invention. The inventors added a treatment, as an experiment, to various types of ink commercially available for manufacturing electronic components using screen-printing. The inventors decreased a viscosity of the inks by dilution; then filtered them by a metallic filter to print them by a commercially available ink jet printer. However, metal powder and ceramic powder included in the ink immediately precipitated, thereby resulting in failure. To avoid forming precipitates, the inventors fed the ink, with application of stirring, to the printer head. This attempt invited clogging of the printer head caused by particles of the ink precipitated in the printer head. As is proved by this attempt, an ink jet apparatus capable of coping with ink having high-concentration, high-density, and low-viscosity that is typified by ink for electronic components to offer reliable printing, has not yet been on the market.
Next will be described inconveniences in printing an electrode onto a ceramic green sheet with a thickness of at most 20 μm. The inventors demonstrated that a solvent of ink penetrates into a ceramic green sheet and causes a short circuit, thereby decreasing a yield of a product. This problem and its measure are disclosed in Japanese Patent No. 2,636,306 and Japanese Patent No. 2,688,644. That is, in a case of employing a ceramic green sheet with a thickness of less than 20 μm, penetration of a solvent of ink through such a thin sheet can cause a short circuit, even if electrodes can be formed by ink jet printing.
Inks employing dye and a metallic salt have been conventionally suggested; however, no suggestion has been made about an ink jet apparatus that can offer reliable printing using ink easily forming precipitates and aggregates, such as ink for manufacturing electronic components. Even if such inks for electronic components as a completed product are filtered by an extremely fine filter, precipitation or aggregates in the ink jet apparatus may result. This fact easily invites clogging of a printer head or ink-spouting section, and as a result, it has been difficult to obtain printing with stability. Of the ink for manufacturing electronic components, the ink employing dye or metal salt can offer relatively good printing. Such inks, however, are intended for coloring, not for manufacturing electronic components such as LC filters and high-frequency electronic components. Besides, in a process of producing laminated ceramic electronic components, and in a case that ink for electrodes is applied onto a thin ceramic green sheet with a thickness of less than 20 μm, a conventional ink jet apparatus has not been successful in providing printing quality with stability. Such inks, due to their property of easily forming precipitates and aggregates, tend to clog the head or the ink-spouting section of an ink jet printer, thereby resulting in inconsistent printing. An effective suggestion to solve the above problems has not yet been made.